This invention pertains to the monitoring of the electrical conductivity in a fluid. For the purpose of explanation herein, a preferred embodiment of the invention is described in conjunction with the monitoring of the electrical conductivity in a dialysate fluid which is used in conventional kidney-patient dialysis.
There are many applications where it is desirable and important to monitor the conductivity of a fluid. Further, there are many such applications wherein it is desirable to be able to accomplish such monitoring without directly contacting, and perhaps interfering with the chemistry of, a fluid.
One application wherein the present invention has been found to have a particular utility is in the monitoring of the dialysate used in kidney-patient dialysis. It is typical during dialysis to mix, on a continuous basis, a dialysate concentrate with water to produce a dialysate fluid having a prescribed concentration. It is important that such concentration be held within certain limits, and thus, monitoring of the condition of the dialysate is also important.
Methods and apparatus have been proposed in the past for such monitoring through following the electrical conditions in the prepared dialysate. However, these various methods either involve direct contact with the dialysate, or have had inherent instability problems which have made it difficult accurately to follow the important minute changes which may be taking place in the mixture.
The present invention proposes a unique apparatus for accomplishing such monitoring while avoiding problems that attend prior art attempts in the same direction.
Thus, a general object of the present invention is to provide electrical apparatus for measuring the conductivity of a fluid, such as a dialysate, which apparatus accomplishes this purpose without requiring contacting of such a fluid, and with means provided for stabilizing the apparatus so as to furnish maximum accuracy.
A preferred embodiment of the invention features measuring apparatus employing fluid-coupled primary and secondary transformer windings, with the primary winding energized by an oscillator. Output signals are derived from the secondary winding. Enhancing the accuracy of the apparatus, and more specifically, minimizing the likelihood of an error being introduced as the result of a change in the signal output level of the oscillator, is a feedback winding which is used in the primary section of the transformer. This feedback winding couples with an output-level control input in the oscillator in such a manner that the output level of the oscillator is stabilized.
Various other objects and advantages which are attained by the invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawing which shows, schematically, the apparatus of the invention set up to monitor the conductivity of a dialysate liquid.